Pneumatic motors



June 28, 1966 H. s. BROOM ET AL PNEUMATIC MOTORS Filed Jan. 25, 1963 United States Patent 3,257,913 PNEUMATIC MOTORS Horace S. Broom and. Howell Bryn Gittins, High Wycombe, England, assignors to Broom & Wade Limited, High Wycombe, England, a British company Filed Jan. 25, 1963, Ser. No. 253,797 Claims priority, application Great Britain, Jan. 30, 1962, r 3,529/ 62; Jan. 27, 1962, 32,877/62 5 Claims. (Cl. 91-76) The present invention comprises improvements in or relating to pneumatic motors.

In pneumatic motors it is usual to control the speed by means of a centrifugal governor so that in the event of the load going 0d, the motor does not run away.- It is possible however for a centrifugal governor to sieze or fail and it is an object of the present invention to provide an additional safety device.

According to the present invention in a pneumatic motor a safety device to prevent overspeeding comprises a valve member to obturate the air admission passage to the motor, .a rotary element driven by the motor and coupled to the valve member to move therewith in the direction of its opening and closing movements, means urging the valve member toward closed position and a centrifugally-released.holding device on the rotary element to restrain the valve member from movement to closed position. By this means the rotary element is normally held up from movement to permit the valve member to close but if an excessive speed is reached the holding device is released and closure of the air passage takes place.

Preferably, the air passage is co-axial with the motor, the valve member takes the form of a sliding sleeve surrounding the air-admission passage and rotating with the motor and the rotary element is formed to .act as one with the sleeve.

Preferably there is also provided a locking coupler' which slides axially on the valve member, couples the holding device for the valve member with the centrifugally-operated element and serves to lock the holding device in position unless centrifugal release takes place.

The following is a description, by way of example, of

on the same plane as FIGURE 1 toparticularly show the overspeed safety device.

The body of the motor comprises a casing 11 in which is a vane-type rotor 12 and air admission ports 13, 14 are cut through the casing '11 on one side and exhaust ports 15 on the other side in known manner. The rotor 12 carries sliding vanes 16 and is slightly eccentric in the bore of the casing 11 so that it touches it at one point of the periphery, the air ports \13, 14 being located on one side of the point of contact .and the exhaust ports on the other side. A sleeve 17 surrounds the casing 11 and is in communication with the exhaust ports. End plates '18, 19 and covers 20, 21 are held against the ends of the casing 11 by screws 22 which pass through the structure from end to end. There may be three or four of such screws of which only one appears in the drawing. 1 The end plates 18, 19 support ball bearings 23, 24 for short shafts 25, 26 which project from the rotor at each end. The shaft 26 has a projecting tongue 27 on the end which engages a slot 28 in a coupling member 29 which drives a tongue 30 on a driving shaft 31 supported in a ball bearing 32. The shaft 31 continues beyond the end of the cap '20 in which it is supported by another bal-l hearing not shown in the drawing and outside the cap the shaft 31 may support a grinding wheel, a drill chuck or be coupled to a reduction gear or otherwise utilised for the power output of the motor. The exhaust can :be let out through holes in the sleeve 17 or may be connected by ports in the end plate 19 to the space 33 within the end cap 20 and thence to the atmosphere in .any way desired. A light protective sleeve 34 encloses the sleeve 17 and extends from one of the end caps to the other.

The end cap 21 is extended to form a handle 35 which is co-axial with the motor and is made hollow and provided with a nipple 36 for connection to an air hose so that the .admission of air to the motor is through the handle. The air passes through an inner sleeve 37 in the handle and enters a plug 38 which is fitted with-a rotatable valve member 39 operable by a finger piece 40 for turning on and cutting off the air supply to the motor by hand. The stub shaft 25 which forms part of the rotor and is supported in the bearing 24 terminates at the end of the hearing but it contains a co-axial screwed sleeve 41 which carries a hollow tubular extension 42 of the shaft 25 and on this extension is mounted a centrifugal governor body 43 in which are pivoted governor weights 44. The governor weights have arms 45 which project inwardly toward the extension sleeve 42 of the rotor shaft and they operate against a control sleeve 46 which slides on the exterior of the extension 42.

The extension sleeve 42 is hollow and receives the air supply which is admitted through the control valve 39, it is provided with ports 47 which admit the air to a chamber 48 formed in the end cap *21 and from the chamber 48 the air passes through ports 49 into the port 13 formed in the casing 11 and thence to the air admission ports 14 to the motor. The sleeve 46 is so located that if the governor weights 44 fly outwards they will move the sleeve 46 across the ports 47 and so reduce the air supply to motor.

Within the screwed sleeve 41 there is a thin sliding spindle 50 which extends [freely through a hole drilled along the axis of the rotor and carries an adjustment nut 51 which [forms an abutment to take thepressure of a spring '52 surrounding the sliding spindle 50. At the other end of the spindle 50 there is secured to it a head 53 which slides in the inner end of the bore of the sleeve 42. This head carries a cross-pin 54 which works in a slot 55 cut in the wall of the sleeve 42. The cross-pin is rivetted into the governor port control sleeve 46 and thus the sleeve 46 is drawn to the right, as viewed in FIGURE 1, by the spring 52 and the spring opposes the action of the governor weights. The speed can therefore'be adjusted by unscrewing the sleeve 41, 42 and adjusting the nut 51, afterwards replacing the parts.

Sliding upon the rotary ported sleeve 42 which extends from the rotor shaft 25 but on the opposite side of the ports 47 from that on which the governor sleeve 42 moves, is a second sleeve 56 which forms part of an overspeed safety device. This second sleeve 56 is formed in one piece with a rotary disc 57. The disc 57 has'a rim 58 which overhangs the rear surface of the disc and within the overhanging portion is a sliding coupler.59 which is urged towards the disc 57 by a spring 60. The coupler 59 slides on the outer surface of the sleeve 56 and is notched out at three points around its internal periphery holes in the safety cut-off sleeve 56. Three retaining balls 63 are fitted in the holes in the sleeve 56 so that they enter the depressions in the tubular extension sleeve 42 of the rotor shaft 25 and they are held therein by the sliding coupler 59 which is notched out to ride over them, as indicated at 64. With the parts in this position the safety cut-off sleeve 56 is not able to move and the motor is permitted to runat any speed which is allowed by the governor 43.

The inclined grooves 61 in the coupler 59 contain three centrifugal balls 65, one side of each of which bears against the back of the inclined grooves and the other side of which bears against the back of the disc 57. The effect of the spring 60 is to push the coupler with its inclined grooves to the right, as viewed in FIGURE 1, and to urge the balls 65 inwards. The effect of centrifugal force is to urge them outwards against the action of the spring 60 and if the speed becomes sufficient the coupler member 59 passes beyond the point at which it restrains the balls 63 and the balls 63 fiy out into little pockets 66 formed in the coupler and leave the sleeve 56 free to be pushed by the spring 60 across the ports 47, thereby stopping the motor. Thus, if for any reason the governor 43 sticks and does not operate, at a certain overspeed the device 57 will operate to prevent motor from being damaged by excessive speed. The motor cannot be restarted until the safety device has been re-set and as this involves taking off the cap 21 it ensures that the defect which caused overspeeding will be examined.

Instead of using three centrifugal balls 65 and three release balls 63, there may be only two of each if desired, working in diametrically-opposed slots in the coupler 59.

We claim:

1. In a pneumatic motor, an overspeed safety device comprising in combination a shaft co-axial with and rotating as one with the motor, an air-admission passage in said shaft, an air-supply port in the shaft in communication with the air-admission passage, a safety cut-off sleeve slidable along the outside of said shaft and having a cut-off edge slidable across the ports, means urging the sleeve to cut-off position, a centrifugally-released holding device normally holding the cut-off sleeve from moving to said cut-off position, and a centrifugal governor which also operates a second sliding sleeve which can obturate the same ports from the opposite side thereof to that on which the cut-off sleeve of the safety device is located.

2. In a pneumatic motor, an overspeed safety device comprising in combination a shaft driven by the motor, an air-admission passage in said shaft, an air-supply port in the shaft in communication with the air-admission passage, a safety cut-off sleeve slidable along the shaft and having a cut-off edge slidable across the ports, means urging the sleeve to cut-off position, centrifugally-released holding means normally holding the cut-off sleeve from moving to said cut-off position, said holding means comprising locking elements carried by the cut-off sleeve which enter recesses in the shaft, a coupler slidable over the locking elements to keep them in locked position, centrifugal means engaging the coupler to urge it toward unlocked position and a spring engaging it to urge it toward locked position.

3. A pneumatic motor having a safety device as claimed in claim 2 wherein the centrifugal means comprise balls and the coupler has inclined surfaces against which the balls bear to urge it toward unlocked position.

4. In a pneumatic motor, an overspeed safety device comprising in combination a shaft driven by the motor, an air-admission passage in the interior of said shaft, an air-supply port from the passage to the exterior of said shaft, a safety cut-off sleeve slidable along the shaft over said ports and having openings in it for locking members, a coupler slidable over said safety cut-off sleeve having internally-facing inclined surfaces, locking members in said openings which engage said inclined surfaces and normally enter locking recesses in the shaft, and a spring surrounding the shaft and acting on the coupler to urge both the coupler and cut-off sleeve in the direction for the latter to close the ports.

5. A pneumatic motor as claimed in claim 4, wherein the shaft driven by the motor is co-axial with and rotates as one with the motor, the cut-off sleeve slides on the outside of said shaft and wherein a centrifugal governor also operates a second sliding sleeve which can obturate the same ports from the opposite side thereof to that on which the cut-off sleeve of the safety device is located.

References Cited by the Examiner UNITED STATES PATENTS 2,402,972 7/1946 Mitchell 9176 2,422,733 6/ 1947 Jimerson 9176 3,002,495 10/1961 Babb et al 91-76 3,043,273 7/1962 Schott 91-76 3,071,115 1/1963 Schott 91-221 X SAMUEL LEVINE, Primary Examiner.

JOSEPH H. BRANSON, JR., Examiner.

F. T. SADLER, Assistant Examiner. 

1. IN A PNEUMATIC MOTOR, AN OVERSPEED SAFTEY DEVICE COMPRISING IN COMBINATION A SHAFT CO-AXIAL WITH AND ROTATING AS ONE WITH THE MOTOR, AN AIR-ADMISSION PASSAGE IN SAID SHAFT , AN AIR-SUPPLY PORT IN THE SHAFT IN COMMUNICATION WITH THE AIR-ADMISSION PASSAGE, A SAFETY CUT-OFF SLEEVE SLIDABLE ALONG THE OUTSIDE OF SAID SHAFT AND HAVING A CUT-OFF EDGE SLIDABLE ACROSS THE PORTS, MEANS URGING THE SLEEVE TO CUT-OFF POSITION, A CENTIFUGALLY-RELEASED HOLDING DEVICE NORMALLY HOLDING THE CUT-OFF SLEEVE FROM MOVING TO SAID CUT-OFF POSITION, AND A CENTRIFUGAL GOVERNOR WHICH ALSO OPERATES A SECOND SLIDING SLEEVE WHICH CAN OBTURATE THE SAME PORTS FROM THE OPPOSITE SIDE THEREOF TO THAT ON WHICH THE CUT-OFF SLEEVE OF THE SAFTEY DEVICE IS LOCATED. 